1. Field of the Invention
The present invention relates generally to an electric generator, and more specifically to a small gas turbine engine with an electric generator.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine is used to drive an electric generator to produce electrical energy. A large industrial gas turbine (IGT) engine, like those used in the power producing industry, is directly connected to an input shaft of an electric generator in order to eliminate the need for a gear box in order to slightly increase the overall engine efficiency and the cost and efficiency. Because of the direct drive connection, the IGT engine needs to operate at the same speed as the generator, which will be 60 Hertz (3,600 rpm) in the USA and 50 Hertz (3,000 rpm) in Europe. This is possible because of the large size of these engines.
However, smaller gas turbine engines are also being used to drive electric generators to produce power, such as in areas without electrical power lines like offshore oil rigs or in military battlefields. A small gas turbine engine that operates around 50,000 rpms will require a gear box to reduce the rotational speed down to a level (3,600 or 3,000 rpm) that is acceptable for a 50 or 60 hertz electric generator. A gear box will wear relatively quickly and require maintenance to replace worn gears before the engine requires service. High speed electric generators are known in which the generator shaft can be directly connected to the high speed shaft of the IGT, but these high speed generators are expensive to produce and difficult to design since they require complex electrical power conditioning electronics to change the frequency of the output power to a desired frequency.